Fig. 7.

Treatment with a pan-RAR inhibitor blocks differentiation into SOX9⁺ salivary epithelium. (A-C‴) Mandibular explants were cultured on either 10 µM retinol, 5 µM BMS493, or vehicle control medium, whole-mount immunostained for E-cadherin and SOX9, and imaged by confocal microscopy. (A′-C′) Volume projections of E-cadherin staining in SMG initiation region, rotated for frontal view, show a bilateral pair of epithelial invaginations samples grown on control and retinol medium, but not on BMS493 medium. Control and retinol treated samples have a bilateral pair of SOX9⁺ expression domains that colocalize with the invaginated epithelium (A″,A‴,B″,B‴). The epithelial SOX9 expression domains are absent in BMS493-treated samples (C″,C‴). (D) SOX9 expression colocalized with epithelial buds was quantified by the intensity sum of the immunofluorescence signal. Average and standard error bars for each group are shown (n=4). Yellow arrowheads indicate epithelium invaginated into underlying mesenchyme, yellow asterisks indicate the absence of epithelial invagination. *P<0.05. m, Meckel's cartilage progenitors. Scale bars: 100 µm.